Static electricity problems with floor coverings such as carpets and rugs are well known. Most people have been shocked upon touching a door knob or other metal object after walking across a carpet.
Various attempts have been made to construct footwear designed to prevent static discharges. One type of footwear employs electrically conductive elements within the shoe structure. An example is in U.S. Pat. No. 3,993,932.
A second type of footwear is a flexible, disposable, and conductive shoe covering as exemplified in U.S. Pat. No. 3,869,647. Here, the entire shoe is convered by the conductive covering.
A third type of footwear includes a grounding strap which contacts both the skin of the person and the floor. This is exemplified in U.S. Pat. No. 3,800,446.
The three types of footwear disclosed above have a common characteristic; namely, they use electrically conductive materials to drain away electric charge as it is generated to prevent a build up sufficient to cause a shock. None of the patents disclose footwear designed to prevent a static charge from being generated.
The root cause of the static electric build up is the frictional contact between the disparate materials making up the person's shoe sole and the floor covering surface which the shoe sole contacts.
Materials have been listed as to their electrostatic properties resulting from frictional contact. This list is called the Triboelectric Series.
Materials important in carpet fibers and shoe soles are listed in their approximate order of electric charge generating potential in the Triboelectric Series in Table I.